This invention relates generally to hermetic refrigeration compressors of the type used in household appliances, and more particularly to suction and discharge muffler systems for single reciprocating piston compressors.
Household refrigerators and freezers generally use relatively low horsepower compressors in the range of 1/6 to 1/3 horsepower, and tend to run the compressor on a relatively long-duty cycle to obtain the necessary cooling, so that under very high ambient temperature conditions, the duty cycle may approach 100 percent. One of the reasons for this approach is not only the low original cost of a relatively small compressor, but also because smaller compressors tend to produce less noise, which is a very important factor with household appliances of this type. Generally, the compressors are of the hermetically sealed type containing a motor compressor unit resiliently mounted on springs within the hermetic case, and employ a single cylinder with a reciprocating piston therein, usually driven by a two-pole motor, so that the operating speeds tend to approach, under relatively low-load running conditions, the maximum speed of 3600 rpm with a 60 Hz power supply. Likewise, for reasons of simplicity of construction and long life, these compressors use reed-type suction and discharge valves to control the flow of gases into and out of the cylinder, and such valves are operated, of course, by the flow of the gas itself, and therefore open and close quite abruptly. Because of the high speed and the action of the valves, as well as the normal pumping action, such compressors tend to make a considerable amount of noise as a result of the gas flow through them, apart from other mechanical noises. Thus, to achieve the desired quietness of operation, it has been necessary to supply suction and exhaust mufflers to silence both the intake of air from inside the casing into the cylinder and the flow of compressed gas out of the discharge valve to the discharge line from the compressor casing. Because the intake pressure is relatively low, the suction valves do not require as much dampening action on the pulses and must allow higher rates of flow, while the discharge valves operate under high pressure but lower volume of compressed gas, so that the construction of the suction and discharge mufflers tends to be quite different.
While normally such mufflers are designed primarily with respect to their effect in quieting the compressor while retaining low cost of manufacture, it has become increasingly important in recent years to increase the overall efficiency of the compressor to thereby increase the overall efficiency of the appliance to obtain at least equal amounts of cooling using less power to drive the compressor. However, it is recognized that with relatively small compressors of the type used in refrigerators and freezers, the design parameters can become quite different from those employed to increase efficiency in much larger compressors such as multiple piston compressors used in large air conditioning installations. Increasing the overall efficiency of a refrigeration compressor must take place generally in one of three areas: first, by increasing the efficiency of the electric motor driving the compressor; second, by decreasing mechanical friction losses in the moving parts; and third, by increasing the volumetric efficiency of the compressor. While volumetric efficiency is affected by a large number of factors, such as the efficiency of the suction and discharge valves, the clearance volume in the cylinder when the piston is at top dead center, and the temperature of the low pressure return refrigerant gas entering the compressor suction, another area where substantial increases in efficiency can be obtained is in the efficiency of the suction and discharge mufflers themselves, i.e., by making such mufflers so that they provide minimum throttling or restriction of gas flow both to and from the cylinder while still providing sufficient silencing of the gas flow, and with a minimum of increase in cost of manufacture of the entire compressor. Likewise, the fact that such compressors must have a generally small outer casing to take up a minimum amount of space within the refrigerator or freezer provides definite limitations in the size and construction of the mufflers, as well as the other parts of the compressor.